Sonoelastography represents one of the most significant new developments in the field of medical imaging and ultrasonic tissue characterization. It has shown great promise in such diverse applications as early tumor detection and vascular elasticity measurement. Unfortunately, current sonoelastic methods are either static or non-quantitative, limiting their application in moving tissues. The ability to dynamically, noninvasively image the viscoelastic properties of muscle could have significant impact on the management of musculoskeletal and cardiovascular disorders. Three approaches to dynamic sonoelastic muscle imaging will be investigated - quasistatic compression, vibration propagation and dynamic compression. Each of these has its advantages and limitations that require further investigation. Through the application of newly developed accurate ultrasonic noise-tolerant motion tracking algorithms along with an in-depth analysis of their sensitivity to noise, these methods will be perfected and their accuracy assessed in soft tissue phantoms. Finite element analysis will be used to explore the nature of wave propagation in the phantoms and in human limbs to better understand the response of each sonoelastic method to specific geometries and arrangements of elastic elements. Human subjects will be used to validate the models developed and to assess the dynamic response to changes in muscle elasticity. Sonoelastography has the potential to provide a new research tool through which the effectiveness of various interventions and rehabilitation strategies can be tested and optimized. It may open new areas of investigation of muscle physiology and pathology never before thought possible.